Filaments over distances up to several kilometers are formed when high-power ultra-short laser pulses are launched in air. They are created by a dynamic interplay between two nonlinear effects, i.e. Kerr self-focusing and subsequent plasma defocusing. Self-phase modulation and self-steepening of the pulse give rise to a strong broadening of the spectrum. The consequence is a white light laser pulse (super continuum). Potential practical applications of these phenomena include lightning discharge control and remote sensing.
It is known in the art to combine LIDAR (Light Detection and Ranging) techniques and time-resolved absorption spectroscopy techniques and apply them to a pulsed broadband light source in order to perform range-resolved multi-trace analyses simultaneously. While this process can be applied to the remote sensing of pollutants in the atmosphere, sensitivity is an issue. Normally, for detecting different pollutant molecules, different lasers with different output wavelengths are required. This causes difficulties especially for the analysis of multi-component mixtures.
There is a need to develop a new scheme of LIDAR technique to detect pollutant molecules in air, or any other transparent medium, with improved sensitivity.